(a) Field of the invention
This invention relates to annular illumination devices to be used for phase-contrast microscopes and super-resolution microscopes.
(b) Description of the invention
For example, as shown in FIG. 1, an optical system of a conventional phase-contrast microscope is formed of an illuminating system consisting of a light source 1, a collector lens 2 and relay lens 3 for making lights coming out of the light source 1 parallel lights, a ring slit 4 arranged in the rear of the relay lens 3 and a condenser lens 5 having a front focal point arranged so as to substantially coincide with the ring slit 4, making the light having passed through the ring slit 4, that is, an annular light a conical light bundle and projecting it diagonally onto an object S and an observing system consisting of an objective 6, a phase plate arranged in a position conjugate with the ring slit 4 with respect to the optical system including the objective 6 and condenser lens 5 so that the image by the condenser lens 5 and objective 6 of the ring slit 4 may overlap on it and an eyepiece not illustrated. However, as the numerical aperture NA of the light passing through the object S is usually about 1/2 the numerical aperture of the objective 6, the magnification of the objective 6 is 10 to 100 times and the numerical aperture varies from 0.25 to 1.25, it has been necessary to vary the diameter of the ring slit 4 in response to the numerical aperture of the objective 6. Therefore, in this kind of conventional illuminating system, usually a plurality of ring slits 4 different in the diameter are concentrically arranged on a rotary plate so that a ring slit of a proper diameter may be properly selected and used by rotating the rotary plate in response to the numerical aperture of the objective 6. However, it has a defect that the operation is difficult. Further, in the case of this illuminating system, only a part of the light rays from the light source 1 will be passed through the ring slit 4. Therefore, there have been problems that the light amount loss is large and that the visual field is dark.